LXR linux/mm/fremap.c

   1/*
   2 *   linux/mm/fremap.c
   3 * 
   4 * Explicit pagetable population and nonlinear (random) mappings support.
   5 *
   6 * started by Ingo Molnar, Copyright (C) 2002, 2003
   7 */
   8#include <linux/backing-dev.h>
   9#include <linux/mm.h>
  10#include <linux/swap.h>
  11#include <linux/file.h>
  12#include <linux/mman.h>
  13#include <linux/pagemap.h>
  14#include <linux/swapops.h>
  15#include <linux/rmap.h>
  16#include <linux/module.h>
  17#include <linux/syscalls.h>
  18
  19#include <asm/mmu_context.h>
  20#include <asm/cacheflush.h>
  21#include <asm/tlbflush.h>
  22
  23static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  24                        unsigned long addr, pte_t *ptep)
  25{
  26        pte_t pte = *ptep;
  27
  28        if (pte_present(pte)) {
  29                struct page *page;
  30
  31                flush_cache_page(vma, addr, pte_pfn(pte));
  32                pte = ptep_clear_flush(vma, addr, ptep);
  33                page = vm_normal_page(vma, addr, pte);
  34                if (page) {
  35                        if (pte_dirty(pte))
  36                                set_page_dirty(page);
  37                        page_remove_rmap(page, vma);
  38                        page_cache_release(page);
  39                        update_hiwater_rss(mm);
  40                        dec_mm_counter(mm, file_rss);
  41                }
  42        } else {
  43                if (!pte_file(pte))
  44                        free_swap_and_cache(pte_to_swp_entry(pte));
  45                pte_clear_not_present_full(mm, addr, ptep, 0);
  46        }
  47}
  48
  49/*
  50 * Install a file pte to a given virtual memory address, release any
  51 * previously existing mapping.
  52 */
  53static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  54                unsigned long addr, unsigned long pgoff, pgprot_t prot)
  55{
  56        int err = -ENOMEM;
  57        pte_t *pte;
  58        spinlock_t *ptl;
  59
  60        pte = get_locked_pte(mm, addr, &ptl);
  61        if (!pte)
  62                goto out;
  63
  64        if (!pte_none(*pte))
  65                zap_pte(mm, vma, addr, pte);
  66
  67        set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
  68        /*
  69         * We don't need to run update_mmu_cache() here because the "file pte"
  70         * being installed by install_file_pte() is not a real pte - it's a
  71         * non-present entry (like a swap entry), noting what file offset should
  72         * be mapped there when there's a fault (in a non-linear vma where
  73         * that's not obvious).
  74         */
  75        pte_unmap_unlock(pte, ptl);
  76        err = 0;
  77out:
  78        return err;
  79}
  80
  81static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
  82                        unsigned long addr, unsigned long size, pgoff_t pgoff)
  83{
  84        int err;
  85
  86        do {
  87                err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
  88                if (err)
  89                        return err;
  90
  91                size -= PAGE_SIZE;
  92                addr += PAGE_SIZE;
  93                pgoff++;
  94        } while (size);
  95
  96        return 0;
  97
  98}
  99
 100/**
 101 * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
 102 * @start: start of the remapped virtual memory range
 103 * @size: size of the remapped virtual memory range
 104 * @prot: new protection bits of the range (see NOTE)
 105 * @pgoff: to-be-mapped page of the backing store file
 106 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 107 *
 108 * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
 109 * (shared backing store file).
 110 *
 111 * This syscall works purely via pagetables, so it's the most efficient
 112 * way to map the same (large) file into a given virtual window. Unlike
 113 * mmap()/mremap() it does not create any new vmas. The new mappings are
 114 * also safe across swapout.
 115 *
 116 * NOTE: the @prot parameter right now is ignored (but must be zero),
 117 * and the vma's default protection is used. Arbitrary protections
 118 * might be implemented in the future.
 119 */
 120asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 121        unsigned long prot, unsigned long pgoff, unsigned long flags)
 122{
 123        struct mm_struct *mm = current->mm;
 124        struct address_space *mapping;
 125        unsigned long end = start + size;
 126        struct vm_area_struct *vma;
 127        int err = -EINVAL;
 128        int has_write_lock = 0;
 129
 130        if (prot)
 131                return err;
 132        /*
 133         * Sanitize the syscall parameters:
 134         */
 135        start = start & PAGE_MASK;
 136        size = size & PAGE_MASK;
 137
 138        /* Does the address range wrap, or is the span zero-sized? */
 139        if (start + size <= start)
 140                return err;
 141
 142        /* Can we represent this offset inside this architecture's pte's? */
 143#if PTE_FILE_MAX_BITS < BITS_PER_LONG
 144        if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 145                return err;
 146#endif
 147
 148        /* We need down_write() to change vma->vm_flags. */
 149        down_read(&mm->mmap_sem);
 150 retry:
 151        vma = find_vma(mm, start);
 152
 153        /*
 154         * Make sure the vma is shared, that it supports prefaulting,
 155         * and that the remapped range is valid and fully within
 156         * the single existing vma.  vm_private_data is used as a
 157         * swapout cursor in a VM_NONLINEAR vma.
 158         */
 159        if (!vma || !(vma->vm_flags & VM_SHARED))
 160                goto out;
 161
 162        if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
 163                goto out;
 164
 165        if (!(vma->vm_flags & VM_CAN_NONLINEAR))
 166                goto out;
 167
 168        if (end <= start || start < vma->vm_start || end > vma->vm_end)
 169                goto out;
 170
 171        /* Must set VM_NONLINEAR before any pages are populated. */
 172        if (!(vma->vm_flags & VM_NONLINEAR)) {
 173                /* Don't need a nonlinear mapping, exit success */
 174                if (pgoff == linear_page_index(vma, start)) {
 175                        err = 0;
 176                        goto out;
 177                }
 178
 179                if (!has_write_lock) {
 180                        up_read(&mm->mmap_sem);
 181                        down_write(&mm->mmap_sem);
 182                        has_write_lock = 1;
 183                        goto retry;
 184                }
 185                mapping = vma->vm_file->f_mapping;
 186                /*
 187                 * page_mkclean doesn't work on nonlinear vmas, so if
 188                 * dirty pages need to be accounted, emulate with linear
 189                 * vmas.
 190                 */
 191                if (mapping_cap_account_dirty(mapping)) {
 192                        unsigned long addr;
 193                        struct file *file = vma->vm_file;
 194
 195                        flags &= MAP_NONBLOCK;
 196                        get_file(file);
 197                        addr = mmap_region(file, start, size,
 198                                        flags, vma->vm_flags, pgoff, 1);
 199                        fput(file);
 200                        if (IS_ERR_VALUE(addr)) {
 201                                err = addr;
 202                        } else {
 203                                BUG_ON(addr != start);
 204                                err = 0;
 205                        }
 206                        goto out;
 207                }
 208                spin_lock(&mapping->i_mmap_lock);
 209                flush_dcache_mmap_lock(mapping);
 210                vma->vm_flags |= VM_NONLINEAR;
 211                vma_prio_tree_remove(vma, &mapping->i_mmap);
 212                vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 213                flush_dcache_mmap_unlock(mapping);
 214                spin_unlock(&mapping->i_mmap_lock);
 215        }
 216
 217        err = populate_range(mm, vma, start, size, pgoff);
 218        if (!err && !(flags & MAP_NONBLOCK)) {
 219                if (unlikely(has_write_lock)) {
 220                        downgrade_write(&mm->mmap_sem);
 221                        has_write_lock = 0;
 222                }
 223                make_pages_present(start, start+size);
 224        }
 225
 226        /*
 227         * We can't clear VM_NONLINEAR because we'd have to do
 228         * it after ->populate completes, and that would prevent
 229         * downgrading the lock.  (Locks can't be upgraded).
 230         */
 231
 232out:
 233        if (likely(!has_write_lock))
 234                up_read(&mm->mmap_sem);
 235        else
 236                up_write(&mm->mmap_sem);
 237
 238        return err;
 239}
 240
 241